Background description includes information that may be useful in understanding the present invention. It is not an admission that any of the information provided herein is prior art or relevant to the presently claimed invention, or that any publication specifically or implicitly referenced is prior art.
Hydrocarbon feed stocks such as petroleum crudes, gas oil, etc. are subjected to various processes in order to isolate and separate different fractions of the feedstock. The lower boiling fractions, including naphtha, from which gasoline is derived, are recovered as an overhead fraction from the distillation column. The fractions with intermediate volatility are withdrawn from the distillation column as sidestreams. Sidestream products include kerosene, jet fuel, diesel fuel, and gas oil. The overhead and sidestream products are cooled, condensed and sent to other units to be processed into final products.
The distillation equipment is liable to corrosive activity of acids such as HCl, H2S, organic acids, and H2CO3. HCl, the most troublesome corrosive material, is formed by hydrolysis of calcium and magnesium chlorides originally present in crude oils. The problem of corrosion caused by these acidic components as water condenses in the overhead condensing system of distillation columns. The water condensate formed contains a significant concentration of these acidic components, and high concentrations of the same render the pH of the water condensate highly acidic and, of course, dangerously corrosive. Accordingly, neutralizing treatments have been used to render the pH of the condensate alkaline to thereby minimize acid-based corrosive attack at those regions of the apparatus with which this condensate is in contact.
The rate of corrosion is directly related to the concentration of hydrogen ions in the water condensate. A particularly difficult aspect of the problem is that corrosion occurs above and in the temperature range of the initial condensation of water. The term “initial condensate” as used herein indicates a phase formed when the temperature of the surrounding environment reaches the dew point of water. At this point a mixture of liquid water, hydrocarbon, and vapor may be present. Such initial condensate may occur within the distilling column itself or in subsequent columns. The top temperature of the fractionating column is normally maintained above the dew point of water. The initial water condensate formed contains a high percentage of HCl. Due to high concentration of acids dissolved in the water, the pH of the first condensate is quite low and the condensed water is highly corrosive.
Several treatment methods using different types of amines, including highly basic amines, have been proposed in the art to control or inhibit corrosion that ordinarily occurs at the point of initial condensation within or after the distillation unit. However, treatment methods utilizing the known amines have not been successful and specific problems have been reported in connection with the use of these amines for treating the initial condensate. For example, U.S. Pat. No. 7,381,319 states that use of highly basic amines such as, morpholine, methoxypropylamine, ethylenediamine, monoethanolamine, hexamethylenediamine, etc. for treating the initial condensate has a problem relating to the resultant hydrochloride salts of these amines which tend to form deposits in various parts of the distillation unit and thereby cause both fouling and under-deposit corrosion problems.
The inability of some neutralizing amines to condense at the dew point of water tend to form a highly corrosive initial condensate and thereby leads to formation of hydrochloride or sulfide salts of those neutralizing amines on metallic surfaces of the distillation columns. The salts appear before the dew point of water result in fouling and under-deposit corrosion, often referred to as “dry” corrosion.
Further, it is difficult to assess the corrosion rate and determining the required dosage of amines during the operating conditions of overhead condensing system. Traditional treatment methods optimize the amine dosage depending on boot water pH, chloride and iron counts, but these methods do not provide information as to optimal dosage of amines for system conditions.
There is thus a need in the art for a new and improved neutralizing agent that facilitates effective neutralization of acidic components at the point of initial condensation and/or minimizes or eliminates deposits of salts on metal surfaces of distillation columns and thereby avoids formation of fouling and under-deposit corrosion. Also, there is a need in the art for a system and method to assess the corrosion rate and to optimize the dosage of neutralizing agents during the operating conditions of overhead condensing system.
The present invention satisfies the existing needs, as well as others, and generally overcomes the deficiencies found in the prior art.